Audio-gd NFB-5, 9 switchable filters - Page 3

What I meant is that FUN has analog in, so you could go soundcard / cd player / whatever analog output -> FUN amp -> speakers / headphone, skipping the FUN's DAC section entirely.

 

The only inputs on the Sparrow/NFB-11/NFB-12/NFB-5 are digital, so it has to be processed by the DAC.

 

 

This is the last real outstanding feature the FUN has over the other units, and why it might possibly cost more. But almost nobody would use it I think, so it makes sense with the changes in the NFB-5 as a successor of the FUN.

Edited by Elanzer - 7/24/11 at 11:24pm

 

I for one use FUN only as an amp. I find the amp section so good that it deserves a better source.
 

 

I wonder what the OPAMP does in this unit? one more buffer stage in between the DAC output and the ACSS?

If it really does and people don't mind of loosing one more stage (which maybe does not necessary anyway), then we have one way to add LINE-IN : take out the OPA2134 opamp, install two RCA socket, wire L and R positive signals to the opamp output pins and wire RCA input grounds to the some low level ground point in the board...

So anytime we select "DAC/HP switch" to 2 and 4, we have line-in and use this unit for headphone amp only, directly go to the ACSS input...

EDIT: hey, even found one point for the signal ground here
Edited by dw1narso - 7/27/11 at 1:51am

Nice idea. You might need to add a couple of resistors in there as a line-level input might be somewhat stronger than the DAC output.

The OPA is a standard configure in a DAC, most DAC products in world had the OPA or similar analogy amps after the D/A chips.

The NFB5,  the D/A chips feed to the headphone amp by balanced ACSS signal if the OPA had bypass , balanced connect can bring out the best performance of the D/A chips . And the D/A chips feed to the amps without OPA is the most neutral sounding.

If the OPA active, the balanced signal from the D/A chips had convert to a single end ACSS signal feed to the headphone amp.

So remove the OPA, addition the RCA input, must transmit the signal to ACSS signal .

 

Edited by Kingwa - 7/27/11 at 9:02am

If I may...

 

What KingWa meant to say is - you can add "standard" single ended RCA inputs, but since NFB-5 gain stage operates in current mode (ACSS) the problem here is to convert voltage signal from those "standard" RCA inputs into ACSS current signal - you would need some kind of input V/I stage for that.

no... that is not he tried to say.,...

he means that the DAC output is actually differential (L+, L- and R+, R-)... You can check this from WM8741 datasheet.. With opamp inplace, the opamp would convert those into single ended before fed into the ACSS. This conversion is what AMB Gamma DAC and Audinst HUD-MX1 do as well. (NOTE: this also mean that there is a coupling capacitor after the opamp to block the DC offset)

On the opamp bypass mode, the differential output would fed directly to ACSS differential input.

Thus, if we add LINE-IN in the place of opamp output pins, we can only connect to ACSS in single ended.... and this is something that I already expect. But at least, we will get single ended ACSS headphone amp... , and I believe he also try to say... "yes you can"

I am using the FUN and I know little about electronics.

 

Now I have a question about OPA. If it is not necessary to use OPA and it will sound more neutral if we bypass the OPA, why do we have to use OPA in the first place??

You don't, it's optional.

Then, what is the advantage of using an OPA? Just to tune the sound signature?

Extra volume for difficult to drive headphones.

 

That's what Kingwa says said.  His budget amps all feature multiple options with which to color the sound to your liking, except NFB-12.

 

For NFB-5, apparently it is just giving option... direct differential from DAC to the ACSS stage, or through the OPA (converted to single ended first) then [via SE to differential converter] to ACSS (which may sound different then straight because of the character influence of the OPA)

For Fun... I don't know... the description on the FUN page is not that clear... maybe FUN owner could help...

FUN/Sparrow appear to require the opamp.

Just to sidetrack a little... I'm surprised nobody has yet to mention that Kingwa is now using SMT for his circuits.